Nitrocellulose composition and process of preparation



United States Office I LIV'UVI MY Ell 106-81 3,188,224 Patented June 8,1965 Delaware No Drawing. Filed Oct. 31, 1961, Ser. No. 148,830 20Claims. (Cl. 106-195) This invention relates to unique, stable,colloidal dispersions, or sols, of nitrocellulose in voltaile organicliquid compositions which are not solvents for nitrocellulose, and tomethods for preparing these colloidal dispersions.

In the usual manufacture of nitrocellulose, the nitrocellulose isobtained as a water-wet mass which is dehydrated by the displacement ofthe water with alcohol, and the product is normally sold in the form ofalcoholwet fibers or cubes. Because the bulk density of nitrocellulosein these forms is relatively low the amount of nitrocellulose that canbe shipped in a container is small in relation to its actual density.

Since the majority of the ultimate uses for nitrocellulose require it tobe in solution, the buyer of alcohol-wet nitrocellulose expendsconsiderable time and labor in dissolving the nitrocellulose in thepreparation of lacquers, adhesives, etc.

It is also well known that utilization of nitrocellulose in lacquers,adhesives, and other important fields of nitrocellulose application hasbeen based from the inception of the art to the present time, on thepractice of dissolving the nitrocellulose in an active nitrocellulosesolvent-or solvent mixture with dilution of the composition with cheaphydrocarbon diluents, insofar as possible, in the interests of economy.Heretofore, however, the maximum amount of cheap hydrocarbon diluentwhich could be used in any particular instance has been limited largelyby the dilution ratio of the particular nitrocellulose solvent beingemployed for the particular hydrocarbon to be utilized for dilution. Inmost applications, however, the amount of hydrocarbon diluent which canbe safely used without encountering precipitation of the nitrocelluloseupon evaporation of the volatile vehicle is somewhat less than themaximum amount determined by dilution ratio. In the interest of moreeconomical formulation practice, therefore, there has been concertedeffort over the years to find means whereby more of the cheaphydrocarbon diluent and less of the considerably more expensive activenitrocellulose solvent can be utilized in nitrocellulose lacquers andother nitrocellulose applications.

It is an object of the present invention to provide a process by whichwater-wet nitrocellulose can be simultaneously dehydrated andtransformed into a flowable concentrate of nitrocellulose in anonaqueous liquid dispersant, thus simplifying the dehydration andachieving economics for the manufacturer.

It is a further object of the invention to provide flowablenitrocellulose concentrates which permit the shipping of a greaterweight of nitrocellulose in standard containers than heretoforepossible, and with greater safety.

It is still another object of the invention to provide flowablenitrocellulose concentrates that are more easily handled and convertedinto finished products by the consumer, particularly from the standpointof the ease with which they can be converted into solutions.

It has now been discovered in accordance with this invention how toprepare clear, homogeneous, viscous, flowable nitrocellulosecompositions in organic liquid vehicles which are substantially higherin hydrocarbon content and substantially lower in active nitrocellulosesolvent content than heretofore known. The unique nitrocellulosecompositions which are obtained by a novel process in accordance withthis invention are colloidal dispersions, or sols, of nitrocellulose inorganic liquid compositions which comprise a major amount of a volatilealiphatic, cycloaliphatic or aromatic hydrocarbon or halogenatedaliphatic hydrocarbon, a minor amount of active nitrocellulose solventand further containing as an essential ingredient a polar organiccompound containing a hydroxyl or keto group that is capable of hydrogenbonding with nitrocellulose molecules and at least one hydrocarbonresidue of more than 3 carbon atoms but less than the number of carbonatoms which reduce the solubility of the polar compound in water tobelow 0.5% by weight in an amount sufiicient to effect formation ofstable sols of nitrocellulose in said organic liquid compositions. Thesestable colloidal dispersions are hereinafter termed nitrocelluloseorganosols to distinguish them from conventional orthodox nitrocellulosesolutions from which they distinguish in several important respects, aswill be pointed out and discussed hereinafter. The proportion of activenitrocellulose solvent to hydrocarbon diluent in the nitrocelluloseorganosols of this invention is substantially below the amount necessaryto form conventional, orthodox nitrocellulose solutions.

Although the new nitrocellulose organosols of this inventionsuperficially resemble orthodox nitrocellulose solutions by being clear,homogeneous, viscous, flowable compositions, they are distinguishablefrom orthodox nitrocellulose solutions in several important respects asfollows:

(I) Unmodified with resins or plasticizers, they produce uponevaporation of the volatile liquid components clear, strongly adherentand substantially nonshrinking films on glass surfaces, whereas orthodoxnitrocellulose solutions unmodified with resins or plasticizers producefilms which exhibit marked shrinkage upon drying and which arenonadherent to glass.

(2) The nitrocellulose organosols of this invention exhibit markedthixotropy, with pronounced temporary reduction of viscosity whensubjected to high shear. This is because these nitrocellulose organosolsare colloidal swollen aggregates of nitrocellulose molecules dispersedin organic liquid systems which have only swelling action on thenitrocellulose. High shear temporarily dissociates these swollenaggregates with consequent reduction of viscosity during application ofthe high shear.

Orthodox nitrocellulose solutions, on the other hand, unless modified byaddition of materials which impart thixotropic properties thereto,normally are not thixotropic. This is because orthodox nitrocellulosesolutions use excessive active nitrocellulose solvents and are trueNewtonian systems in which the nitrocellulose in substantiallymolecularly dissolved in the solvent.

(3) The nitrocellulose organosols of this invention can be dilutedsubstantially with a lean mixture of such as 4:1 by volume mixture of avolatile aromatic hydrocarbonzaliphatic alcohol mixture, e.g., 4:1toluenezbutyl alcohol, without coagulation or separation of thenitrocellulose from the diluted composition, and the thus dilutedcomposition upon evaporation also produces clear, strongly adherent,substantially nonshrinking films on glass. Orthodox nitrocellulosesolutions, on the other hand, will tolerate only limited dilution withlean mixtures such as hydrocarbomalcohol mixtures, the amount of suchdilution being governed largely by the dilution ratio characteristic ofthe active solvents present in the nitrocellulose solution. Greaterdilution results in coagulation and separation of the nitrocellulosefrom the solution.

The capacity of the nitrocellulose organosols of this invention fordilution with lean hydrocarbomalcohol mixtures without precipitation ofthe nitrocellulose, combined with the capacity for such dilutedorganosol compositions to form clear, adherent, nonshrinking films uponevaporation are essential characteristics of these organosolcompositions, and are of great economic significance in the formulationand application of nitrocellulose coatings, adhesives, and the like.

The process in accordance with this invention for preparing the newnitrocellulose organosols comprises forming a nitrocellulose solution inan organic liquid vehicle comprising a volatile nitrocellulose solventhaving a boiling point below about 65 C., and a volatile, liquidhydrocarbon selected from the group consisting of aliphatic,cycloaliphatic, and aromatic hydrocarbons, and halogenated aliphatichydrocarbons having a boiling point substantially above about 65 C., theproportion of said volatile nitrocellulose solvent to said volatileliquid hydrocarbon being substantially in excess of the dilution ratiocharacteristic of said volatile nitrocellulose solvent for said volatileliquid hydrocarbon, evaporating said volatile nitrocellulose solventfrom said nitrocellulose solution at a temperature up to about 65 C.,and preferably at reduced pressure, until said volatile nitrocellulosesolvent remaining therein is reduced to an amount between about 50% byweight, based on the weight of nitrocellulose, and a lower amount atwhich incipient phase separation begins, and adding at any stage of theprocess a polar organic compound containing a hydroxyl or keto groupthat is capable of hydrogen bonding with nitrocellulose molecules and atleast one hydrocarbon residue of more than 3 carbon atoms but less thanthe number of carbon atoms which reduce the solubility of the polarcompound in water to below 0.5% by weight in an amount within the rangebetween about 0.1 and about 125 parts per part of nitrocellulose byweight, and preferably between about 0.1 and about 0.5 part. In thisprocess, therefore, the polar organic compound can be present in thenitrocellulose solution, or can be added during the volatilenitrocellulose solvent removal or can be added upon completion ofvolatile nitrocellulose solvent removal. In a preferred and economicalembodiment of the process in accordance with this invention, water-wetnitrocellulose is subjected to azeotropic distillation in the presenceof a volatile aromatic hydrocarbon until all water has been removed toproduce an aromatic hydrocarbon-wet nitrocellulose prior to formation ofthe nitrocellulose solution.

Nitrocellulose organosols containing up to 50% by weight ofnitrocellulose have been prepared by the above process.

Nitrocellulose organosols in accordance with this invention can also beprepared by direct high shear mixing of the ingredients of thenitrocellulose organosol composition, as for example, in a Baker-Perkinsmixer.

In the preparation of the new nitrocellulose organosols, it ispostulated that the polar organic compound having a hydrophobichydrocarbon residue orients itself at the interface between the solventswollen nitrocellulose molecules and the hydrocarbon phase by hydrogenbonding of the polar group thereof to residual hydroxyl groups in thenitrocellulose, with the hydrophobic hydrocarbon residue thereoforiented outwardly in the hydrocarbon phase. The nitrocellulose sol isthus believed to be stabilized by the hydrophobic layer of the polaradditive which shields the nitrocellulose from the diluent duringstripping off of active nitrocellulose solvent, or during dilution ofthe organosol with lean solvents, or during evaporation of the volatilevehicle in the process of film formation.

It is apparent, therefore, that the polar organic compound having ahydrophobic hydrocarbon residue is essential and must meet certainrequirements to be suitable for the purposes of this invention. Morespecifically, the polar group of the compound must be capable of stronghydrogen bonding with residual hydroxyl groups present in thenitrocellulose and with active hydrogen atoms adjacent to the nitratesubstituent groups in the nitrocellulose in order to form a stableinterfacial shield between the nitrocellulose and the hydrocarbondiluent. Moreover, the hydrocarbon residue of the polar compound shouldhave sufiicient hydrophobic capacity to promote compatibility with thehydrocarbon phase, without, however, being so strongly hydrophobic as topromote desorption of the polar compound away from the interfacialboundary of the nitrocellulose into the hydrocarbon phase. It is wellknown, of course, that the hydrophobic character of polar organiccompounds increases with increasing length or size of the hydrocarbonresidue. In general, it had been found that polar compounds havingmethyl, ethyl, propyl, and isopropyl hydrocarbon residues do not havesufficient hydrophobic capacity for the purposes of this invention,whereas polar compounds having heptyl, octyl and higher hydrocarbonresidues have excessive hydrophobic capacity for the purposes of thisinvention. Thus, when the hydrocarbon residue of the polar compound isan acyclic aliphatic residue it should contain from 4 to 6 carbon atoms.On the other hand, when the hydrocarbon residue is wholly or in partcycloaliphatic, it can contain from 6 to 8 carbon atoms. In any event,the proper balance of polar and hydrophobic groupings in such compoundsshould be such as to give it a solubility of at least 0.5%, by weight,in water.

Polar organic compounds having a hydrophobic hydrocarbon residue whichmeet the requirements of this invention have been found to includeprimary straight chain aliphatic alcohols having from 4 to 6 carbonatoms in the alkyl group, such as butyl, amyl and hexyl alcohols;monoalkyl ethers of ethylene glycol and diethylene glycol having 4 to 6carbon atoms in the alkyl groups, such as the monobutyl, monoamyl andmonohexyl ethers of ethylene glycol and diethylene glycol; alkyl estersof hydroxycarboxylic acids having 4 to 6 carbon atoms in the alkylgroups, such as butyl, amyl and hexyl lactates, dibutyl, diamyl anddihexyl tartrates, tributyl, triamyl and trihexylcitrates, and the like;cycloaliphatic alcohols and ketones having 6 to 8 carbons in thehydrocarbon residue, such as cyclohexanol, methyl cyclohexanol, ethylcyclohexanol, and cyclohexanone, methyl cyclohexanone, ethylcyclohexanone; also camphor and benzyl alcohol; and mixtures of any suchcompounds.

The most preferred polar organic compound having a hydrocarbon residuefor the purposes of this invention is n-butanol. Other preferred polarorganic compounds include cyclohexanol, dibutyltartrate, and themonobutyl ether of ethylene glycol. Less preferred polar organiccompounds include amyl and hexyl alcohols and other polar organiccompounds containing amyl or hexyl radicals, since the greaterhydrophobicity of these compounds requires their use in larger amountsto accomplish the purposes of this invention. For example, the followingtable shows the amount of each of several ditferent polar organiccompounds which it was found necessary to add to a solvent-strippedconcentrate obtained by solvent stripping a nitrocellulose solutioncontaining Parts by weight Nitrocellulose 21 Ethyl alcohol 9 Acetone 70Toluene to the first sign of haziness in order to prepare nitrocelluloseorganosols exhibiting satisfactory clear, adherent, nonshrinking filmformation characteristics:

The polar compound having a hydrocarbon residue is present in thecompositions of this invention in an amount sufiicient to efiectformation of stable sols of nitrocellulose in the organic liquidcompositions employed, and this is generally within the range betweenabout 0.1 and about 1.25 parts per part of nitrocellulose by weight,preferably between about 0.1 and about 0.5.

The polar compound need not be present in the original nitrocellulosesolution before stripping otf the volatile nitrocellulose solvent inorder to effect formation and stabilization of the nitrocelluloseorganosol upon stripping the volatile solvent from the solution.However, the presence of the polar compound during stripping ispreferred. Since a small amount of moderately volatile polar compoundsuch as butanol is evaporated from the solution during stripping of thevolatile nitrocellulose solvent therefrom, it is desirable to add suchmoderately volatile polar compound to the solution in an amount inexcess over the amount necessary or desired in the final nitrocelluloseorganosol, the excess being added to compensate for the amountevaporated during stripping.

Stripping of the volatile nitrocellulose solvent from the nitrocellulosesolution may be carried out at any convenient temperature up to about 65C. Temperatures appreciably above about 65 C. tend to promotedegradation of the nitrocellulose. It is desirable to employtemperatures near or above the boiling point of the volatilenitrocellulose solvent in order to promote rapid stripping of thesolvent. For the same reason, it is desirable, but not necessary, tostrip the solvent under sub-atmospheric pressure. Stripping is continueduntil the amount of volatile nitrocellulose solvent remaining in thecomposition is below about 50% by weight, based on the weight ofnitrocellulose. If desired, stripping may be carried to the point whereincipient phase separaion in the organosol composition is noticed asevidenced by formation of haze. Stn'pping beyond this point isundesirable, since it leads to pronounced phase separation andnonhomogeneity in the organosol composition. Since the weight andcomposition of the starting nitrocellulose solution are known, it ispossible to follow the course of the stripping operation by collectingand analyzing the stripped volatiles. The composition of the strippedvolatiles may be quickly estimated by diluting with a large volume ofwater and measuring the volume of the insoluble fraction in a graduatedcylinder. Additional information on composition can be obtained bychromatographic analysis. Because of the difiiculty in completelycondensing the stripped highly volatile nitrocellulose solvent, theanalytical information in the subsequent examples, if anything, err onthe side of showing more volatile nitrocellulose solvent in the strippedconcentrates than is actually present.

Substantially all of the commercial types and grades of nitrocelluloseare suitable for the purposes of this invention having nitrogen contentsfrom about 10.9% to about 13.5% nitrogen, and viscosity characteristicsfrom centipoise type to 1000 second type. One-half /2) second typenitrocellulose having 12% nitrogen content has been employed in theexamples, since this is widely used in the formulation of lacquers andother protective coatings, adhesives, inks, and the like.

This invention requires the use of a volatile nitrocellulose solventhaving a boiling point below about 65 C. in order to facilitate removalthereof by means of solvent stripping. Acetone is the preferred solventbecause of its active solvent action on nitrocellulose and ease ofremoval by stripping. However, any solvent for nitrocellulose which hasa boiling point below about 65 C. is suitable, and includes by way ofexample, methyl alcohol, methyl formate, ether-alcohol mixtures, and thelike.

Any volatile liquid hydrocarbon compound having a boiling pointsubstantially above 65 C. is suitable for the purposes of thisinvention, including by way of example, straight and branched chainaliphatic hydrocarbons such as heptane, isooctane, decane, decene,petroleum spirits, and the like; cycloaliphatic hydrocarbons such ascyclohexane, methyl cyclohexane, ethyl cyclohexane, and the like;aromatic hydrocarbons such as benzene, toluene, xylene, and the like;various halogenated aliphatic hydrocarbons such as ethylene dichloride,perchlooroethylene, tetrachloroethane, tribromoethylene, and the like;and mixtures thereof. The boiling point requirement is to insureretaining as much as possible of the hydrocarbon compound in theorganosol compositions through the solvent stripping step. Toluene ispreferred, since it is widely used in lacquer and protective coatingapplications because of its desirable evaporation characteristics,solvency for numerous resins and plasticizers, and other well knowncharacteristics.

The mixtures of volatile nitrocellulose solvent and volatile liquidhydrocarbon employed to prepare the nitrocellulose solution obviouslymust be active solvent mixtures for the nitrocellulose. This means,therefore, that the proportion or ratio of volatile nitrocellulosesolvent to volatile liquid hydrocarbon in such mixtures must besubstantially in excess over the dilution ratio characteristic of thevolatile nitrocellulose solvent for the volatile liquid hydrocarbon. Theamount of such volatile nitrocellulose solvent-volatile liquidhydrocarbon mixture employed is at least sutficient to form a fluid,stirrable nitrocellulose solution, and is generally within the rangefrom about 3 to about 10 parts by weight of the mixture for each part byweight of nitrocellulose, depending somewhat on the viscositycharacteristic of the nitrocellulose, and the desired percentage ofnitrocellulose in thefinal nitrocellulose organosol produced. It is arelatively simple matter to select the composition and amount of suchvolatile nitrocellulose solvent-volatile liquid hydrocarbon mixture forpreparing the nitrocellulose solution, which after stripping willproduce a nitrocellulose organosol having the desired nitrocellulosecontent.

It has been found that the nitrocellulose organosols of this inventionare readily adapted to conventional lacquer and protective coatingapplications, since, in addition to their unique capacity for toleratingdilution with hydrocarbon-alcohol mixtures, they can be readily modifiedwith a wide range of conventional resins, plasticizers, softeningagents, pigments and fillers, and similar modifying agents fornitrocellulose coating compositions. Moreover, if desired, they can bethinned with conventional nitrocellulose solvents. These nitrocelluloseorganosols, prior to thinning with hydrocarbon-alcohol mixtures arestable with respect to phase separation indefinitely, and can thereforebe stored and shipped as desired. After thinning and modifying withsuitable resins, plasticizers and the like, the thinned compositions canbe applied by any of the conventional methods of application, such asspraying, brushing, dipping, roller coating, and the like.

The general nature of the invention having been set forth, the followingexamples illustrate some specific embodiments of the invention. It is tobe understood, however, that the invention is in no way limited to theexamples, since this invention may be practiced by the use of variousmodifications and changes within the scope of the invention as describedherein.

Example I (A) A nitrocellulose solution was prepared with 30 parts byweight of ethyl alcohol-wet 36 second nitrocellulose of 12% nitrogencontent and containing approximately 30% by weight of denatured ethylalcohol, 70 parts by weight of acetone, and parts by weight of toluene.This solution while being stirred was solvent stripped in a vacuumvessel at approximately 60 C. under a vacuum of approximately 100 mm. ofmercury until 100 parts by weight of volatiles had been stripped fromthe solution. The stripped volatiles were collected in two Dry Icecooled traps, combined, and subjected to chromatographic analysis, whichindicated the combined volatiles to contain approximately 6 parts byweight of Nitrocellulose 21 Denatured ethyl alcohol 3 Toluene 65.5Acetone This stripped concentrate prepared in the absence of a polarorganic compound showed very pronounced phase separation and dried to achalky film. However, upon the addition of 9 parts by weight ofcyclohexanol, a clear, homogeneous, viscous liquid resulted which driedwithout shrinking to a clear, adherent film on glass. It also exhibitedthixotropy.

(B) The procedure of A was repeated, except that the originalnitrocellulose solution contained 9 parts by weight of cyclohexanol. Thestripped concentrate was a clear, homogeneous, viscous fluid which driedto a clear, continuous, adherent film on glass. The stripped concentratewas calculated to contain Parts by weight Nitrocellulose 21.0 Denaturedethyl alcohol 3.0 Cyclohexanol 9.0 Toluene 65.5 Acetone 10.0

This stripped concentrate exhibited thixotropy.

To 10 grams of the above stripped concentrate was added cc. of a diluentcomposed of Cc. Toluene 43 Butyl acetate 4 Acetone 4 Ethyl alcohol 1Parts by weight 40 10 the resulting diluted organosol composition wasclear, homogeneous and fluid, and upon evaporation produced a clear,adherent, nonshrinking film on glass.

Toluene n-Butanol Example 2 A nitrocellulose solution was prepared with90 parts by weight of butanol-wet /2 second nitrocellulose of 12%nitrogen content and containing approximately 30% by weight ofn-butanol, 210 parts by weight of acetone, 120 parts by weight oftoluene, and 6 parts by weight of dibutyltartrate. This solution whilebeing stirred was solvent stripped in a vacuum vessel at approximately60 C. under a vacuum of approximately 100 mm. of mercury untilapproximately 275 parts by weight of volatiles had been stripped fromthe solution. Based on chromatographic analysis of the strippedvolatiles, the resulting stripped concentrate, amounting toapproximately 151 parts by weight was calculated by difference tocontain:

Percent by weight This concentrate was clear, homogeneous flowablenitrocellulose organosol which exhibited thixotropy and which uponevaporation produced a clear, adherent, nonshrinking film on glaSS.

To 10 grams of the above concentrate was added 13 cc. of a diluentconsisting of Cc. Toluene 40 n-Butanol 10 The resulting dilutedcomposition was a clear, homogeneous flowable nitrocellulose organosolexhibit thixotropy which upon evaporation produced a clear, adherent,nonshrinking film on glass.

Example 3 Sixty (60) parts by weight of water-wet /2 secondnitrocellulose having 12% nitrogen content and containing approximately30% by weight of water were immersed in 258 parts by weight of xyleneand subjected to azeotropic distillation under a vacuum of approximatelymm. of mercury until 206 parts by weight of volatiles had been removedand analysis of the stripped volatiles showed that all water in thenitrocellulose had been removed. To the xylene-nitrocellulose mixtureremaining, consisting of Parts by weight Nitrocellulose 42 Xylene 70Percent by weight Nitrocellulose 40.4 Cyclohexanol 19.2 Acetone 14.7Xylene 25.7

This concentrate was a clear, homogenous flowable nitrocelluloseorganosol exhibiting thixotropy, which upon evaporation produced aclear, adherent, nonshrinking film on glass.

To 10 grams of the above concentrate was added 13 cc. of a diluentconsisting of Toluene 40 n-Butanol 10 The resulting diluted organosolcomposition exhibiting thixotropy was clear, homogeneous and fluid, andupon evaporation produced a clear, adherent, nonshrinking film on glass.

Example 4 A nitrocellulose solution was prepared with 30 parts by weightof ethyl alcohol-wet /2 second nitrocellulose having 12% nitrogencontent and containing approximately 30% by weight of ethyl alcohol, 70parts by weight of acetone, 10 parts by weight of the mono-n-butyl etherof ethylene glycol, and 40 parts by weight of toluene. This solutionwhile being stirred was solvent stripped in a vacuum vessel atapproximately 60 C. under a vacuum of approximately 100 mm. of mercuryuntil approximately 91 parts by weight of volatiles had been strippedfrom the solution. Based upon chromatographic analysis of the strippedvolatiles, the resulting stripped concentrate was calculated to containPercent by weight Nitrocellulose 35.5 Mono-n-butyl ether of ethyleneglycol 16.9 Acetone 11.3 Ethyl alcohol 5.1 Toluene 31.2

Toluene 40 n-Butanol 10 The resulting diluted organosol compositionexhibiting thixotropy was clear, homogeneous and fluid, and uponevaporation produced a clear, adherent, nonshrinking film on glass.

Example Substantially the same procedure as set forth in Example 3 wasfollowed, employing toluene instead of xylene to azeotropically stripwater from the water-wet nitrocellulose. To the toluene-nitrocellulosemixture remaining after stripping off the water, and consisting of 42parts by weight nitrocellulose and 70 parts by weight toluene was added20 parts by weight cyclohexanol and 140 parts by weight acetone to forma nitrocellulose solution. This solution was then stripped of volatilesby the same procedure set forth in Example 3 until the final weight ofthe stripped concentrate was 90 parts by weight, containing 46.7% byweight of nitrocellulose.

This stripped concentrate was a clear, homogeneous, very viscousfiowable nitrocellulose organosol exhibiting thixotropy which uponevaporation produced a clear, adherent, nonshrinking film on glass.

To grams of the above concentrate was added 13 cc. of diluent consistingof Cc. Toluene 40 n-Butanol 10 A nitrocellulose solution was preparedwith 90 parts by weight of isopropyl alcohol-wet /2 secondnitrocellulose having 12% nitrogen content and containing approximately30% by weight of isopropyl alcohol, 210 parts by weight of acetone, 132parts by weight of perchloroethylene, and 20 parts by weight ofdibutyltartrate. This solution while being stirred was solvent strippedin a vacuum vessel at approximately 60 C. under a vacuum ofapproximately 100 mm. of mercury until 352 parts by weight of volatileshad been stripped from the solution, and the stripped concentrateremaining weighed 100 parts by weight. Based on analysis of the strippedvolatiles, the composition of the stripped concentrate was calculated bydifierence to contain Percent by weight Nitrocellulose 35.6Di-n-butyltartrate 1 1.3 Perchloroethylene 30.0 Acetone 12.0 Isopropanol11.1

Cc. Toluene 40 n-Butanol 10 The resulting diluted organosol compositionexhibiting thixotropy was clear, homogenous and fluid, and uponevaporation produced a clear, adherent, nonshrinking film on glass.

Following substantially the procedure set forth above, clear,homogeneous flowable nitrocellulose organosols were propared withheptane, and with isooctane, in place of perchloroethylene. Theheptane-containing and isooctane-containing organosols each exhibitedthixotropy and each formed clear, adherent, nonshrinking films on glassupon evaporation, and each, when diluted with a diluent consisting of 40cc. toluene and 10 cc. n-butanol, as set forth for theperchloroethylene-containing organosol, as set forth above, was a clear,homogeneous flowable fluid exhibiting thixotropy which upon evaporationproduced clear, adherent, nonshrinking films on glass.

Example 7 A nitrocellulose solution was prepared with 30 parts by weightof ethyl alcohol-wet /2 second nitrocellulose having 12% nitrogencontent and containing approximately 30% by weight of ethyl alcohol, 70parts by weight of acetone, parts by weight of toluene, and 10 parts byweight of cyclohexanol. This solution while being stirred was solventstripped in a vacuum vessel at approximately 60 C. under a vacuum ofapproximately 100 mm. of mercury until the first incipient sign of phaseseparation (faint cloudiness) was noticed. At this point approximately116 parts by weight of volatiles had been stripped from the solution,and stripping was discontinued. Approximately 1 cc. of ethyl alcoholadded to the stripped concentrate caused disappearance of thecloudiness. Based upon chromatographic analysis of the strippedvolatiles, the composition of the stripped concentrate was calculated bydifference to contain Parts by weight Nitrocellulose 21.0 Cyclohexanol9.7 Acetone 10.0 Ethyl alcohol 2.9 Toluene 41.1

This stripped concentrate was a clear, homogeneous viscousnitrocellulose organosol exhibiting thixotropy, which dried to a clear,adherent, nonshrinkiing film on glass.

To 10 grams of the above stripped concentrate was added 15 cc. of adiluent consisting of The resulting diluted organosol composition wasclear, homogeneous and fluid, and upon evaporation produced a. clear,adherent, nonshrinking film on glass.

Following substantially the same procedure set forth above, clear,homogeneous, viscous nitrocellulose organosol compositions exhibitingthixotropy were prepared with cyclohexanone, camphor, monobutyl ether ofethylene glycol, monobutyl ether of diethylene glycol, and benzylalcohol in place of cyclohexanol, and these organosols showedsubstantially the same dilution characteristics and film-formingcharacteristics as set forth above for the nitrocellulose organosolcontaining cyclohexanol.

By contrast, however, when cyclohexanol was replaced by acetone,diacetone alcohol, Cellosolve acetate (ethoxyethylacetate) butylacetate, 2-ethylhexylacetate, dibutylphthalate, butyl Cellosolve acetate(butoxyethylacetate), monoethyl ether of diethylene glycol, monoethylether of ethylene glycol, methyl isobutyl carbinol, or cetyl alcohol,satisfactory nitrocellulose organosols in accordance with this inventionwere not obtained.

This example clearly demonstrates that it is not the capacity of thepolar compound to function as nitrocellulose solvents which determinessuitability for the purposes of this invention, since esters such asbutyl acetate, ethoxyethyl acetate, 2-ethyl hexyl acetate, andbutoxyethyl acetate, known to be good solvents for nitrocellulose,nevertheless failed to produce nitrocellulose organosols having thecharacteristics of this invention. On the other hand, cyclohexanol,butanol, benzyl alcohol, amyl alcohol, and hexyl alcohol, recognized ashaving no solvency for nitrocellulose, have clearly been demonstrated bythe examples to produce satisfactory nitrocellulose organosols inaccordance with this invention. The evidence is clear, therefore, thatit is the capacity of polar organic compounds to form an interfacialprotective layer between solvent-swollen nitrocellulose molecules andthe diluent phase by hydrogen bonding between the hydroxy or keto groupsof the polar organic compound and the nitrocellulose molecules whichdetermines suitability for the purposes of this invention, and not thecapacity of the polar organic compound to function as a nitrocellulosesolvent.

Example 8 A nitrocellulose solution was prepared with 29.4 parts byweight of n-butanol-wet second nitrocellulose having 12% nitrogencontent and containing 28.5% by weight of n-butanol, 4.6 parts by weightof additional n-butanol, 40 parts by weight of toluene, and 70 parts byweight of acetone. This solution while being stirred was solventstripped in a vacuum vessel under a vacuum of 18 to 20 inches of mercurywhile gradually raising the temperature of the solution from roomtemperature to approximately 54 C. until 88 parts by weight of volatileshad been stripped from the solution. Based on chromatographic analysisof the stripped volatiles, the resulting stripped concentrate wascalculated by diflerence to contain Percent by weight Nitrocellulose37.3 n-Butanol 19.0 Acetone 11.1 Toluene 32.6

This concentrate was a clear, homogeneous fiowable nitrocelluloseorganosol exhibiting thixotropy, which upon evaporation produced aclear, adherent, nonshrinking film on glass.

To grams of the above concentrate was added 13 cc. of a diluentconsisting of Ce. Toluene 40 n-Butanol 10 The resulting dilutedorganosol composition exhibiting thixotropy was clear, homogeneous andfluid, and produced upon evaporation a clear, adherent, nonshrinkingfilm on glass.

Example 9 A stable nitrocellulose organosol composition was prepared bycharging a Baker-Perkins mixer with the following ingredients and thenmixing until the resulting composition was homogeneous:

Parts by weight of V2 second nitrocellulose of 12% nitrogen content andcontaining 30% by weight of denatured ethyl alcohol 115.3 Parts byweight of cyclohexanol 38.4 Parts by weight of acetone 23.2 Parts byweight of toluene 44.9

Ce. Toluene 40 n-Butanol 10 The resulting diluted organosol compositionwas clear, homogeneous and flowable, and upon evaporation produced aclear, adherent, nonshrinking film on glass.

From the foregoing description, it is apparent that the presentinvention provides new and unique nitrocellulose compositions havingimportant advantages over previously known compositions, and alsoprovides methods for their manufacture. An important characteristic andadvantage of these new compositions is their capacity to be successfullythinned with hydrocarbon-alcohol mixtures, so that the thinned mixturescan contain as high as 70- 75% of hydrocarbon diluent. For the lacquerformulator this makes possible a substantial reduction in the cost ofmaking lacquers and other protective coatings with nitrocellulose.Moreover, since the new compositions of this invention are viscous,flowable, colloidal dispersions of nitrocellulose in organic liquidvehicles, there are further economies for the formulator in that he doesnot require means for dissolving the usual dehydrated fibrous or cubednitrocellulose. Mixing time in formulating finished lacquers and coatingcompositions is therefore markedly reduced, since it is only necessaryto add the required thinner, resin solution, plasticizer, etc., andblend by stirring for a few minutes.

For the nitrocellulose manufacturer, this invention provides a new andeconomical form for supplying nitrocellulose to the trade, since agreater weight of nitrocellulose as nitrocellulose organosol containingon the order of to by weight of nitrocellulose can be shipped in astandard container than is possible with conventional dehydrated fibrousor cubed nitrocellulose. There are also manufacturing economies in thepresent invention in processing water-wet nitrocellulose into a formsuitable for use by the nitrocellulose forrnulator.

I claim:

1. As a new composition, a colloidal dispersion of nitrocellulose in anorganic liquid composition containing from about 20% to about 50% byweight of nitrocellulose, said organic liquid composition consistingessentially of (a) a major amount of a volatile hydrocarbon compoundselected from the group consisting of aliphatic, cycloaliphatic andaromatic hydrocarbons, halogenated aliphatic hydrocarbons, and mixturesthereof, having a boiling point above C.,

(b) a minor amount, at least about 20% and not exceeding about 50% byweight, based on nitrocellulose weight, of a volatile nitrocellulosesolvent having a boiling point below about 65 C., the ratio of saidhydrocarbon to said volatile nitrocellulose solvent being at least about1.5 and not more than about 6.6 by weight,

(c) and containing as an essential ingredient a polar organic compoundhaving a polar group selected from the class consisting of hydroxyl andketo groups that is capable of hydrogen bonding with nitrocellulosemolecules and at least one hydrocarbon residue of more than 3 carbonatoms but less than the number of carbon atoms which reduce thesolubility of said polar organic compound in water to below 0.5% byweight in an amount from about 0.1 to about 1.25 parts per part byweight of nitrocellulose, and suflicient to effect formation of a stablesol of said nitrocellulose in said organic liquid composition,

said colloidal dispersion of nitrocellulose being characterized by (1)being a clear, homogeneous, flowable, thixotropic material,

(2) the capacity to tolerate dilution without separation of thenitrocellulose when 10 grams of said colloidal dispersion are dilutedwith 15 cc. of a 4:1 by volume mixture of a volatilehydrocarbon:aliphatic alcohol mixture,

(3) and the capacity to produce clear, adherent, non- 13 shrinking filmson glass and also when diluted as described in (2) above.

2. A composition in accordance with claim 1 in which the polar organiccompound is butanol.

3. A composition in accordance with claim 1 in which the polar organiccompound is dibutyltartrate.

4. A composition in accordance with claim 1 in which the polar organiccompound is cyclohexanol.

5. A composition in accordance with claim 1 in which the polar organiccompound is the mono-n-butyl ether of ethylene glycol.

6. A composition in accordance with claim 1 in which the volatilehydrocarbon compound is an aromatic hydrocarbon.

7. A composition in accordance with claim 1 in which the volatilehydrocarbon compound is an aliphatic hydrocarbon.

8. A composition in accordance with claim 1 in which the volatilehydrocarbon compound is a halogenated aliphatic hydrocarbon.

9. A composition in accordance with claim 1 in which the volatilenitrocellulose solvent is acetone.

10. A process for preparing stable colloidal dispersions ofnitrocellulose comprising (1) forming a nitrocellulose solution in anorganic liquid vehicle consisting essentially of (a) a volatilenitrocellulose solvent having a boiling point below about 65 C. and (b)a volatile liquid hydrocarbon compound selected from the groupconsisting of aliphatic, cycloaliphatic, and aromatic hydrocarbons,halogenated aliphatic hydrocarbons, and mixtures thereof, having aboiling point above about 65 C., the proportion of said volatilenitrocellulose solvent to said volatile liquid hydrocarbon compoundbeing substantially in excess of the dilution ratio characteristic ofsaid volatile nitrocellulose solvent for said volatile liquidhydrocarbon,

(2) evaporating said volatile nitrocellulose solvent from saidnitrocellulose solution at a temperature up to about 65 C. until saidvolatile nitrocellulose solvent remaining therein is reduced to anamount between about 50% by weight, based on the weight ofnitrocellulose, and a lower amount at which incipient phase separationbegins and the ratio of said hydrocarbon to said volatile nitrocellulosesolvent is at least about 1.5 and not more than about 6.6 by weight,

(3) and adding at any stage of the process a polar organic compoundcontaining a polar group selected from the class consisting of hydroxyland keto groups that is capable of hydrogen bonding with nitrocellulosemolecules and at least one hydrocarbon residue of more than 3 carbonatoms but less than the number of carbon atoms which reduce thesolubility of said polar organic compound in water to below 0.5% byweight in an amount from about 0.1 to about 1.25 parts per part byweight of nitrocellulose.

11. A process in accordance with claim in which the polar organiccompound is butanol.

12. A process in accordance with claim 10 in which the polar organiccompound is dibutyltartrate.

13. A process in accordance with claim 10 in which the polar organiccompound is cyclohexanol.

14. A process in accordance with claim 10 in which the polar organiccompound is the mono-n-butyl ether of ethylene glycol.

15. A process in accordance with claim 10 in which the volatilenitrocellulose solvent is acetone and the volatile liquid hydrocarbon istoluene.

16. A process in accordance with claim 10 in which step (2) of theprocess is carried out under subatmospheric pressures.

17. A process in accordance with claim 10 in which step (3) of theprocess is carried out by incorporating the polar organic compound inthe nitrocellulose solution before performing step (2) of the process.

18. A process in accordance with claim 10 in which step (3) of theprocess is carried out by incorporating the polar organic compound intothe nitrocellulose composition after performing step (2) of the process.

19. A process for preparing stable colloidal dispersions ofnitrocellulose comprising (1) subjecting water-wet nitrocellulose toazeotropic distillation in the presence of a volatile aromatichydrocarbon until all water is removed to produce an aromatichydrocarbon-wet nitrocellulose,

(2) forming a nitrocellulose solution from the aromatic hydrocarbon-wetnitrocellulose in an organic liquid vehicle consisting essentially of(a) a volatile nitrocellulose solvent having a boiling point below about65 C. and (b) a volatile liquid hydrocarbon compound selected from thegroup consisting of aliphatic, cycloaliphatic, and aromatichydrocarbons, halogenated aliphatic hydrocarbons, and mixtures thereof,having a boiling point above 65 C., the proportion of said volatilenitrocellulose solvent to said volatile liquid hydrocarbon compoundbeing substantially in excess of the dilution ratio characteristic ofsaid volatile nitrocellulose solvent for said volatile liquidhydrocarbon,

(3) evaporating said volatile nitrocellulose solvent from saidnitrocellulose solution at a temperature up to about 65 C. until saidvolatile nitrocellulose solvent remaining therein is reduced to anamount between about 50% by weight, based on nitrocellulose weight, anda lower amount at which incipient phase separation begins and the ratioof said hydrocarbon to said volatile nitrocellulose solvent is at leastabout 1.5 and not more than about 6.6 by weight,

, (4) and adding at any stage of the process, after step (1) above, apolar organic compound containing a polar group selected from the classconsisting of hydroxyl and keto groups that is capable of hydrogenbonding with nitrocellulose molecules and at least one hydrocarbonresidue of more than 3 carbon atoms but less than the number of carbonatoms which reduce the solubility of said polar organic compound inwater to below 0.5 by weight in an amount from about 0.1 to about 1.25parts per part of nitrocellulose by weight.

20. A process for preparing stable colloidal dispersions ofnitrocellulose comprising subjecting to high shear mixing a mixture ofabout 20% to about 50% by weight of nitrocellulose and the balance anorganic liquid composition consisting essentially of (a) a major amountof a volatile hydrocarbon compound selected from the group consisting ofaliphatic, cycloaliphatic and aromatic hydrocarbons, halogenatedaliphatic hydrocarbons, and mixtures thereof, having a boiling pointabove 65 C.

(b) a minor amount, at least about 20% and not exceeding about 50% byweight, based on nitrocellulose weight, of a volatile nitrocellulosesolvent having a boiling point below about 65 C., the ratio of saidhydrocarbon to said volatile nitrocellulose solvent being at least about1.5 and not more than about 6.6 by weight, and

(c) a. polar organic compound having a polar group selected from theclass consisting of hydroxyl and keto groups that is capable of hydrogenbonding with nitrocellulose molecules and at least one hydrocarbonresidue of more than 3 carbon atoms but less than the number of carbonatoms which reduce the solubility of said polar organic compound inwater to below 0.5% by weight in an amount from about 0.1 to about 1.25parts per part by weight of nitrocellulose, and sufiicient to efiectformation of a stable sol of said nitrocellulose in said organic liquidcomposition, said colloidal dispersion of nitrocellulose beingcharacterized by (1) being a clear, homogeneous, flowable, thixotropicmaterial,

(2) the capacity to tolerate dilution without separation of thenitrocellulose when 10 grams of said colloidal dispersion are dilutedwith 15 cc. of a 4:1 by volume mixture of a volatilehydrocarbonzaliphatic alcohol mixture,

(3) and the capacity to produce clear, adherent, nonshrinking films onglass and also when diluted as described in (2) above.

1 6 References Cited by the Examiner UNITED STATES PATENTS 12/40 Donlan106-191 11/55 Johnson 106198 4/56 Voris 106-470 11/57 Sloan l06-17O 7/58Voris 106-170 FOREIGN PATENTS 8/34 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner. 15 MORRIS LIEBMAN, Examiner.

1. AS A NEW COMPOSITION, A COLLODIAL DISPERSION OF NITROCELLULOSE IN ANORGANIC LIQUID COMPOSITION CONTAINING FROM ABOUT 20% TO ABOUT 50% BYWEIGHT OF NITROCELLULOSE, SAID ORGANIC LIQUID COMPOSITION CONSISTINGESSENTIALLY OF (A) A MAJOR AMOUNT OF A VOLATILE HYDROCARBON COMPOUNDSELECTED FROM THE GROUP CONSISTING OF ALIPHATIC, CYCLOALIPHATIC ANDAROMATIC HYDROCARBONS, HALOGENATED ALIPHATIC HYDROCARBONS, AND MIXTURESTHEREOF, HAVING A BOILING POINT ABOVE 65*C., (B) A MINOR AMOUNT, ATLEAST ABOUT 20% AND NOT EXCEEDING ABOUT 50% BY WEIGHT, BASED ONNITROCELLULOSE WEIGHT, OF A VOLATILE NITROCELLULOSE SOLVENT HAVING ABOILING POINT BELOW ABOUT 65*C., THE RATIO OF SAID HYDROCARBON TO SAIDVOLATILE NITROCELLULOSE SOLVENT BEING AT LEAST ABOUT 1.5 AND NOT MORETHAN ABOUT 6.6 BY WEIGHT, (C) AND CONTAINING AS AN ESSENTIAL INGREDIENTA POLAR ORGANIC COMPOUND HAVING A POLAR GROUP SELECTED FROM THE CLASSCONSISTING OF HYDROXYL AND KETO GROUPS THAT IS CAPABLE OF HYDROGENBONDING WITH NITROCELLULOSE MOLECULES AND AT LEAST ONE HYDROCARBONRESIDUE OF MORE THAN 3 CARBON ATOMS BUT LESS THAN THE NUMBER OF CARBONATOMS WHICH REDUCE THE SOLUBILITY OF SAID POLAR ORGANIC COMPOUND INWATER TO BELOW 0.5% BY WEIGHT IN AN AMOUNT FROM ABOUT 0.1 TO ABOUT 1.25PARTS PER PART BY WEIGHT OF NITROCELLULOSE, AND SUFFICIENT TO EFFECTFORMATION OF A STABLE SOL OF SAID NITROCELLULOSE IN SAID ORGANIC LIQUIDCOMPOSITION, SAID COLLOIDAL DISPERSION OF NITROCELLULOSE BEINGCHARACTERIZED BY (1) BEING A CLEAR, HOMOGENEOUS, FLOWABLE, THIXOTROPICMATERIAL, (2) THE CAPACITY TO TOLERATE DILUTION WITHOUT SEPARATION OFTHE NITROCELLULOSE WHEN 10 GRAMS OF SAID COLLOIDAL DISPERSION AREDILUTED WITH 15 CC. OF A 4:1 BY VOLUME MIXTURE OF A VOLATILEHYDROCARBON:ALIPHATIC ALCOHOL MIXTURE, (3) AND THE CAPACITY TO PRODUCECLEAR, ADHERENT, NONSHRINKING FILMS ON GLASS AND ALSO WHEN DILUTED ASDESCRIBING IN (2) ABOVE.